In semiconductor technology, Group III-Group V (or III-V) semiconductor compounds are used to form various integrated circuit devices, such as high power field-effect transistors, high frequency transistors, high electron mobility transistors (HEMTs), and metal-insulator-semiconductor field-effect transistors (MISFETs). An E-HEMT is an enhancement mode field effect transistor incorporating a junction between two materials with different band gaps (i.e., a heterojunction) as the channel instead of a doped region, as is generally the case for metal oxide semiconductor field effect transistors (MOSFETs). In contrast with MOSFETs, HEMTs such as E-HEMTs, have a number of attractive properties including high electron mobility and the ability to transmit signals at high frequencies. However, metal atoms deposited to form metal gates used in HEMTs can diffuse down into device layers, especially during higher temperature manufacturing, and degrade some electrical properties of the HEMTs.